Abstract 9: Distinct types of human colon cancer initiating cells contribute to primary tumor and metastasis formation

Abstract

Abstract Strong evidence indicates that rare tumor initiating cells (TICs) within tumors play a pivotal role in initiation and maintenance of genetically and morphologically heterogeneous human colon cancers. Self-renewing TICs form serially transplantable tumors that resemble the original patient tumor in immunodeficient mice. Up to now, it is unknown whether TICs represent a homogeneous population with identical potential to self-renew and metastasize, or if they are organized in a hierarchically structured cancer stem cell compartment. Here we demonstrate an unexpected cellular heterogeneity within the TIC compartment by lentiviral marking and in vivo clonal tracking of individual, highly enriched primary human colon cancer initiating cells. TICs derived from different primary human colon tumors or metastases were enriched as tumor spheres under serum-free culture conditions. Frequency of cells capable of forming new tumor spheres after replating ranged from 4%-60% depending on the individual patient. In vivo self-renewal and metastatic capacity of single primary colon TICs in serially transplanted tumors and associated metastases were analyzed by highly sensitive tracking of individual lentivirally marked clones. Primary tumor cells were serially transplanted under the renal capsule of immunodeficient NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ (IL2RGnull) mice. Clonal contribution of TICs individually marked by unique lentiviral integration sites was detected by linear amplification-mediated PCR (LAM-PCR) followed by next generation high throughput sequencing. Three distinct types of TICs contributed to tumor formation: 1) previously unnoticed tumor transient amplifying cells (T-TACs) with limited or no self-renewal capacity contributing only to tumor formation in primary mice, 2) rare extensively self-renewing long-term tumor initiating cells (LT-TICs) that maintain tumor formation after serial transplantation and 3) ‘dormant’ TICs that become active in secondary or tertiary mice. Only a subfraction of all TIC clones metastasized into bone marrow or liver, indicating that tumor initiation, self-renewal as well as metastasis forming potential are independently regulated in TICs. Our results allow for the first time detailed insights into the clonal heterogeneity within the human colon cancer initiating cell compartment and identify three distinct types of TICs with different self-renewal and metastasis-forming potential. They indicate that tumor initiation, self-renewal and metastasis formation of TICs are independently regulated. Understanding the regulatory mechanisms underlying self-renewal capacity and metastasis formation in LT-TICs will have important implications for future curative treatment strategies in human colon cancer. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 9.